Conventionally, for satellite communication and meteorological observation, antennas (parabola antennas) having a parabolic reflector are used in some cases. Patent Document 1 discloses such parabola antenna.
The parabola antenna of Patent Document 1 includes a power feeding waveguide, a horn, a parabola reflector, and a reflective plate. A radio wave to be outwardly radiated is transmitted through the power feeding waveguide and radiated from the horn toward the parabola reflector. The horn is disposed at a focal point of a parabolic surface of the parabola reflector and, therefore, the parabola reflector reflects this radio wave as a planar wave. Moreover, the reflective plate is disposed to cancel the reflection on the horn caused by the parabola reflector or the power feeding waveguide. Note that, this reflective plate is formed into a stepped shape.
Thus, Patent Document 1 has a configuration in which the radio wave radiated from the horn is reflected on the parabola reflector to outwardly radiate the radio wave (a configuration having a single reflector). On the other hand, Patent Document 2 discloses a configuration having two reflectors.
An antenna device of Patent Document 2 uses a reflective plate (a sub reflection mirror) to reflect a radio wave radiated by a primary radiator and then uses a lens antenna (or a parabola antenna, a main reflection mirror) to further reflect the radio wave, so as to outwardly radiate the radio wave. Note that, this reflective plate has a configuration of which shape can be changed and a fixed beam pattern can be maintained even if a scanning angle is changed.